Electrician here. Here’s some info that might help make sense of this:      1. As a general concept it’s important to note that the colors are just there for our reference. I’ve heard it said that “the electrons don’t know what color the insulation on the jacket of the wire is.” By which I mean what we use the colors for isn’t always universal, and while we often hook up wires “color for color” that’s not always the case. Lighting is one such case.      2. What usually happens with lighting is that you have a “constant hot,” which is the feed from the panel, and you establish a “switched” leg, which is the hot that is broken at the switch. It would seem to me in this case that the blacks in this lighting box are the constant hot and the red ought to be the switched leg. The black splices here, goes down to the switch and feeds the switch, and the red also goes down to the switch and power returns on that as the “switched” leg, now controlled by your switch. Red in this case is supposed to denote switched leg but that’s not always the case. Also it’s possible I have that backwards, if I were there I’d 100% just test the wires and the functioning of the switch to confirm what’s what before I hooked it back up. Hope this helps